The present invention relates to a cooktop or hob with a cooktop plate, in particular, made from glass ceramic, beneath which at least one heating element is disposed, for heating a cooking vessel that can be placed on the cooktop plate, and having a temperature sensor for recording the temperature of the cooktop plate, which temperature sensor senses the temperature of the underside of the cooktop plate within the heating element and is shielded from the thermal radiation from a heating device of the heating element by insulating material, and is connected to a control unit for controlling the heating power of the heating element, and to a corresponding heating element and a suitable element.
German Patent DE 37 03 768 C2, corresponding to U.S. Pat. No. 4,851,645 to Wolf et al., discloses a device for recording the temperature of a glass ceramic plate that is heated by heating windings or halogen lamps using a temperature sensor. The Wolf device emits a signal that corresponds to the temperature of the glass ceramic to a control circuit. The heating windings or the halogen lamps are disposed in the interior of a pot-like insulating support and heat the glass ceramic plate by direct radiation. The edge of the insulating support bears against the underside of the glass ceramic plate under spring stress, and the temperature sensor is disposed outside the interior of the insulating support but inside the heating element. Furthermore, the temperature sensor is connected in a thermally conductive manner to the underside of the glass ceramic plate, the temperature sensor being disposed in a recess in the edge of the insulating support. The recess is disposed at a distance x from the inner side of the edge of the insulating support, the minimum value for which distance is selected such that the brief temperature changes that occur when the heating windings or the halogen lamps are switched on or off have only a negligible influence on the temperature sensor. The maximum value for the distance x is selected such that the delay in the control characteristic that is caused by the thermal conduction of the glass ceramic plate results in a small hysteresis. Widths from 3 mm to 6 mm have proven to be advantageous values for the distance x. The temperature sensor is introduced into the formed or pressed-in recess on the upper side of the attachment that projects into the interior of the insulating support, and is connected in a thermally conductive manner to the underside of the glass ceramic plate. The temperature sensor is held indirectly through spring stress against the underside of the glass ceramic plate to keep the heat transfer resistance between the glass ceramic plate and the temperature sensor low.
Furthermore, European Patent Application EP 0 021 107 A1. discloses a heating element for a cooker unit having a temperature sensor. To maintain complete heating of the entire surface of the heating element while, nevertheless, closely coupling the temperature sensor of the controller to the heating, a heat transfer element in the form of a metal sheet is used, which is disposed between the heating bodies and the glass ceramic plate, partially covering the heated area, but projects out of the heating element, where it is connected to the temperature sensor of the controller. The heat-transfer element is fastened by secure clamping on the edge of the shell carrying the heating device and normally bears against the underside of the glass-ceramic panel. An outer section projects outward, beyond the edge of the heating element, from the area of the heat transfer element that senses the heat. The outer section is formed integrally with the above mentioned area, substantially parallel thereto, but offset downward to a slight extent by a bend, so that the outer section does not bear against the underside of the glass ceramic plate. The sensor cell of the temperature sensor is pressed by a compression spring onto the underside of the heat-transfer surface of the heat-transfer element, which is supported against a holding mechanism that guides the sensor cell and is disposed on the outer section of the heat-transfer element. However, other sensor types and configurations are also possible. For example, it is also possible to use an electrical NTC or PTC sensor that is pressed on resiliently or securely attached to the outer portion of the heat transfer element. If desired, the heat transfer element may be grounded so that electric shocks are prevented.
Furthermore, U.S. Pat. No. 4,447,710 to McWilliams discloses a glass ceramic cooktop in which an insulating body, on which a temperature sensor, for example, a thermocouple, is positioned, is disposed in the edge region of the heating element. The thermocouple is kept in good thermal contact with the underside of the glass ceramic plate by the insulating block.
It is accordingly an object of the invention to provide a cooktop with temperature sensor and a corresponding heating element that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that have good measuring accuracy.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a cooktop, including a glass ceramic cooktop panel having an underside, at least one heating element having a heating device for emitting thermal radiation, the heating element disposed beneath the cooktop panel for heating up a cooking vessel to be placed on the cooktop panel, a control unit electrically connected to the at least one heating element for controlling a heating power of the at least one heating element, a temperature sensor electrically connected to the control unit for controlling the heating power of the at least one heating element, a heat-conducting element holding the temperature sensor in heat-conducting contact at the underside of the cooktop panel within the at least one heating element, the temperature sensor sensing a temperature of the underside of the cooktop panel within the at least one heating element, and insulating material shielding the temperature sensor and the heat-conducting element from the thermal radiation. The insulating material can also substantially shield the temperature sensor and the heat-conducting element from the thermal radiation.
According to the invention, in the cooktop, the temperature sensor is in thermal contact with the underside of the cooktop plate by a thermally conductive element, and the element and the temperature sensor are shielded from the thermal radiation of the heating device by insulating material. Such a configuration ensures that the measuring configuration determines a temperature that, for example, corresponds to the temperature of a pan that has been placed on the cooktop plate above the heating element quickly and accurately enough. It is also ensured that the heat transfer from the pan or the cooktop plate to the temperature sensor is not limited to the very small area of the temperature sensor itself.
In accordance with another feature of the invention, the surface region A of the element that is in thermal contact with the underside of the cooktop plate is approximately at least 5 times, in particular, approximately 10 times larger than the base area B of the temperature sensor.
In accordance with a further feature of the invention, a lateral distance a between the element and the edge region of the insulating material is advantageously approximately 6 to 12 mm, in particular, approximately 8 mm. This value has surprisingly emerged if, on one hand, the shielding with respect to the thermal radiation from the heating device of the heating element is to be sufficiently great and if, on the other hand, the coupling of the thermally conductive element to the cooktop plate heated by the thermal radiation is to be sufficiently good.
In accordance with an added feature of the invention, to make it possible to provide ratios that are constant and defined by metrology over the operating life of the heating element, the temperature sensor is secured to the element, in particular, is secured to the element by being cast into the element.
To enable the element to be mounted quickly and without problems, the thermally conductive element is secured, in particular, by screw connection, in the region of the outer peripheral wall of the heating element or the insulating support, directly or with the aid of an intermediate mounting part. In particular, it is possible for the intermediate mounting part to be secured in the base region of the heating element and to extend into the region of the outer peripheral wall of the heating element in which the element is, in turn, screwed to the intermediate mounting part. To allow the pressure and the pressing area of the element, and, therefore, inter alia, the thermal coupling of the element to the underside of the cooktop plate, to be set correctly, it is possible for the element to be screwed to the outer peripheral wall of the heating element at different heights.
In accordance with an additional feature of the invention, the temperature sensor is secured to the underside of the element. On one hand, the configuration allows a large, flat bearing surface to be achieved to improve the conduction of heat from the underside of the glass ceramic plate to the temperature sensor. On the other hand, the temperature sensor is provided with better mechanical protection by the larger-area element during the mounting process, for example, when the element/temperature sensor unit is dropped.
To simplify mounting, the element may have a receiving section for the temperature sensor and a mounting section for securing the element, in particular, in the heating element, the receiving section lying laterally offset in the radial direction with respect to the mounting section. Such a configuration is important, in particular, if the temperature sensor is to be mounted in the immediate vicinity of a temperature limiter that is present at the heating element. This is because the temperature limiter restricts the mounting space in the region of the outer peripheral wall of the heating element, but, on the other hand, it is advantageous if the various electrical connections of the temperature limiter and the temperature sensor lie as close together as is permitted under safety regulations.
In accordance with yet another feature of the invention, the heat-conducting element has an underside, the temperature sensor is secured to the underside of the heat-conducting element, and the heat-conducting element is pressed onto the underside of the cooktop panel.
The element advantageously is in at least two-parts. In such a case, a receiving part for the temperature sensor is of a relatively soft material to allow the receiving part to be deformed with an optimum specific geometry in terms of its application and safety regulations. The remainder of the element may be of another material, with, in particular, a spring material being suitable to allow the element to be pressed in a defined manner onto the underside of the glass ceramic plate.
In terms of production and mounting technology, it is particularly favorable if the element is formed as a torsion spring, the torsion region of the spring element being provided substantially outside the heating element and, therefore, in a cooler region.
In accordance with yet a further feature of the invention, the heat-conducting element is a spring element and, limited to a region of the temperature sensor, pressed onto the underside of the cooktop panel.
In accordance with yet an added feature of the invention, the heat-conducting element has an upper wall and side walls and is approximately shroud-shaped at least in a region of the temperature sensor. The side walls of the heat-conducting element are skirt shaped.
In accordance with yet an additional feature of the invention, the heat-conducting element has a shroud with a bottom side and the shroud is at least partly closed on the bottom side.
According to a preferred embodiment, the element is configured to be electrically conductive and is grounded to optimally satisfy the safety regulations while having a simple structure.
To make mounting easier, and, in particular, for strain relief, the electrical lines of the temperature sensor are connected to a first connection section of the element or a connection piece mounted there. Accordingly, the element may also have a second connection section, to which a grounding line of the element is connected.
In accordance with again another feature of the invention, the heat-conducting element is a removable part of the at least one heating element.
With the objects of the invention in view, in a cooktop having a glass ceramic cooktop panel with an underside, at least one heating element having a heating device for emitting thermal radiation and disposed beneath the cooktop panel for heating up a cooking vessel to be placed on the cooktop panel, a control unit electrically connected to the at least one heating element for controlling a heating power of the at least one heating element, and a temperature sensor sensing a temperature of the underside of the cooktop panel within the at least one heating element, in heat-conducting contact with the underside of the cooktop panel within the at least one heating element, and electrically connected to the control unit, there is also provided a temperature sensor holder including a heat-conducting element holding the temperature sensor in heat-conducting contact at the underside of the cooktop panel within the at least one heating element and insulating material substantially shielding the temperature sensor and the heat-conducting element from the thermal radiation of the heating device.
With the objects of the invention in view, in a cooktop having a glass ceramic cooktop panel with an underside, a control unit, and a temperature sensor electrically connected to the control unit, there is also provided a heater including at least one heating element having a heating device for emitting thermal radiation, the at least one heating element electrically connected to the control unit for controlling a heating power of the at least one heating element and disposed beneath the cooktop panel for heating up a cooking vessel to be placed on the cooktop panel, a heat-conducting element holding the temperature sensor in heat-conducting contact at the underside of the cooktop panel within the at least one heating element to sense a temperature thereof, and insulating material substantially shielding the temperature sensor and the heat-conducting element from the thermal radiation of the heating device.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a cooktop with temperature sensor, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.